```go
package main

import (
	"bufio"
	"fmt"
	"os"
)

func main() {
	in := bufio.NewReader(os.Stdin)
	out := bufio.NewWriter(os.Stdout)
	defer out.Flush()

	var t int
	fmt.Fscan(in, &t)

	for i := 0; i < t; i++ {
		var n int
		fmt.Fscan(in, &n)
		var a, b string
		fmt.Fscan(in, &a)
		fmt.Fscan(in, &b)

		c00, c01, c10, c11 := 0, 0, 0, 0
		for j := 0; j < n; j++ {
			if a[j] == '0' {
				if b[j] == '0' {
					c00++
				} else {
					c01++
				}
			} else {
				if b[j] == '0' {
					c10++
				} else {
					c11++
				}
			}
		}

		ans := -1

		// Strategy 1: Even number of operations (pair swaps)
		// We can fix mismatches if the count of (1,0) equals (0,1).
		if c10 == c01 {
			ans = 2 * c10
		}

		// Strategy 2: Odd number of operations
		// Perform one operation on a matching '1' (type 11), then fix remaining with swaps.
		// Requires c11 == c00 + 1. Cost is 1 + 2*c00.
		if c11 == c00+1 {
			res := 2*c00 + 1
			if ans == -1 || res < ans {
				ans = res
			}
		}

		fmt.Fprintln(out, ans)
	}
}
```